Barack Obama finally gave his big climate speech Tuesday — the one environmentalists have been waiting for since he first took office.

But even his biggest proposals fall short of what environmentalists had been hoping for, and what he came into the White House promising to achieve.

Obama once pushed for an ambitious cap-and-trade bill, and pledged to eliminate the generous tax loopholes for oil and gas companies. Now, he’s offering new rules for power plants and energy efficiency — steps environmentalists praise, though hardly the sweeping agenda they’d once envisioned.

It seemed like an achievable goal then, as the cap-and-trade bill passed by the Democratic House made its way through the Senate. But when that bill died in the summer of 2010, it became clear that the window for bold legislative action was closing. When Republicans won a majority in the House and Democrats lost seats in the Senate, it slammed shut.

At stake now: his environmental legacy, a record whose most prominent entries are currently an increase in fuel emission standards for cars, and a failure to pass a House-approved cap-and-trade bill through the Senate in 2009.

“The first several years of his presidency were based on an assumption that Congress could find a compromise that he could sign,” Israel said. “If he can’t get a farm bill passed, how can you expect to get a climate change bill passed? He realized he had to do something.”

“It’s about his legacy, but it’s also about the pressure on his left for him to do something,” said former EPA administrator and New Jersey Gov. Christine Todd Whitman, a Republican. “He needs to appeal to them, and calm down the people who are upset about this.”

Washington Gov. Jay Inslee, a Democrat who served in the House before winning the state house last November, said Obama’s executive action-driven environmental push is a golden opportunity for Obama to focus on a legacy-building exercise: addressing a long-term issue, instead of fighting the political battles of the day.

“They’re not going to worry about some of our fiscal challenges — but when they think of us 80 years from now, if we don’t solve these problems, our names are going to be mud,” Inslee said.

Obama reiterated a longstanding offer Tuesday to work with members of all parties “to make sure that we deal with climate change in a way that promotes jobs and growth. Nobody has a monopoly on what is a very hard problem.”

And Sen. Bernie Sanders (I-Vt.), who in February introduced a carbon tax bill, said Obama will have to engage with Congress if he wants to leave office with a meaningful record of environmental accomplishments.

“Clearly the Congress is going to have to appropriate money and create priorities to do what needs to be done. The president is going to have to demand from Congress a substantial sum of money for energy efficiency,” Sanders said. “If you’re prepared to make it a major priority, I think we need leadership there.”

But the agenda of executive actions the president laid out Tuesday acknowledged the futility of actually trying to reach a workable compromise with recalcitrant Republicans.

Rep. Henry Waxman (D-Calif.), the top Democrat on the House Energy and Commerce Committee, said the unilateral presidential action Obama planned to pursue was a distant second choice — but, at the moment, the only choice.

“It’s not my preference to see this all go by way of executive action,” he said. “But we’ve got to get on with the job, and that’s what the president is doing.”

Like his retreats from the ambitious to the achievable on gun control and the economy, Obama’s environmental agenda has been colored by fact that there’s only so much he can do when saddled with an intransigent House populated with more than a few members who refuse to concede his central premise: that global warming is man-made.

And, just as with the president’s gun control push, the biggest challenge isn’t the inside game — it’s figuring out an effective workaround. Polls show vast majorities of Americans support the concept of climate change action. The problem: They don’t spend all that much time thinking about it, with the issue regularly ranking last in importance.

At the least, the president’s supporters are hoping the president’s focus on the issue will draw attention to what they see as the absurdity of climate change deniers’ views — to make sure climate change skeptics launch Todd Akin-esque headlines.

“The Republicans making a big deal about these rules will be politically beneficial for the president and Democrats,” said Daniel J. Weiss, director of climate strategy at the Center for American Progress. “Every time they say climate change isn’t real, they’re painting themselves into a climate science denial corner that will be difficult to escape from.”

Rep. Gerry Connolly (D-Va.), who with Israel is a co-chairman of the House Sustainable Energy and Environment Coalition, said Obama’s climate push is as much about elevating the environment as an issue for the 2014 midterm elections as it is enacting the far-reaching new regulations he sought in the first term.

“What’s a president to do when you’re dealing with a bunch of luddites who simply will not acknowledge the compelling evidence in front of us?” Connolly said. “I think Obama feels he has no other choice.”

To that end, Obama’s political arm, Organizing for Action, last month began a campaign to shame members of Congress who deny the existence of climate change. And Obama, who welcomes debates on topics ranging from electronic surveillance to mental health services, said Tuesday said he will not entertain arguments about the legitimacy of his environmental actions.

”I don’t have much patience for anyone who denies that this challenge is real,” Obama said. “We don’t have time for a meeting of the Flat Earth Society.”

That line may have won him applause on the left. Another chunk of his Obama’s Tuesday speech drew a cooler response: the section addressing the Keystone pipeline, the biggest — and thorniest — environmental question facing him at the moment.

Keystone opponents have been pressuring the White House to deny the pipeline, which would ferry oil from Canada to Houston for export. Obama said Tuesday he would approve the pipeline’s construction only if the move will not result in a net increase of greenhouse gas emissions.

Not good enough, say some of the president’s strongest supporters. Tom Steyer, a San Francisco-based billionaire who hosted fundraisers for Obama’s 2012 campaign and has discussed a public campaign against the pipeline, told POLITICO Tuesday that the provisos in the climate speech do not absolve the president of his responsibility to block the pipeline.

“President Obama took the moral high ground in his speech today, leading the United States and the world on climate action, and ringing the death knell for the Keystone pipeline,” Steyer said. “He recognizes that the pipeline would damage climate by locking in a 50-year dirty tar sands supply. The president has heard the Keystone critics, and we accept his invitation to keep the pressure on.”

Former Vice President Al Gore, who has been critical of Obama for slow action on climate change, took a more measured line: The proposals Obama laid out Tuesday, he said, “are in keeping with the current political reality.”